1. Field of the Invention
The present invention relates to a laser beam printer, and more particularly a laser beam printer which can stabilize the images to be produced on a photosensitive member by a diode laser in accordance with image data.
2. Description of the Prior Art
The drive device for a diode laser used for a laser printer usually conducts optical modulation for the diode laser based on image signals representing character information or the like from an electronic computer, and the modulated beam is projected onto a photosensitive drum by scanning optical system to produce images on the drum according to the image signals (see, for example, U.S. Pat. No. 4,469,430).
The light output of the diode laser involves variations due to variations in the ambient temperature, adversely affecting the quality of images when the laser is used for laser printers or the like. To compensate for the output variations due to variations in the ambient temperature, it has been proposed to attach a Peltier element to a semiconductor laser to maintain the laser at a constant temperature (as disclosed, for example, in Unexamined Japanese Patent Publication SHO No. 57-63879), or to detect the light output of a diode laser and control the current through the laser based on the result so as to maintain a constant light output despite variations in the ambient temperature (e.g. Unexamined Japanese Patent Publications SHO No. 57-136382 and SHO No. 57-112089). However, the compensation achieved by these proposals is not fully satifactory.
Further with conventional laser printers, the sensitivity of the photosensitive member to be exposed to the laser beam for writing varies with the ambient temperature. Consequently, even if it is possible to maintain the light output of the diode laser at a constant value, the density of images on the photosensitive member varies with variations in the ambient temperature and cannot be maintained at a predetermined level. The prior art nevertheless is still unable to solve this problem.